The mathematical model that the software uses provides options to model noise
emissions from a wide range of sources that might be present at industrial areas
and urban areas. The basis of the model is the linear sound propagation
equation, which is used to model simple point source emissions from vehicles,
industries, aircrafts,… Emission sources are categorized into two basic types of
sources: point sources and line sources. The algorithms used to model each of
these source types are described in detail in the following sections. The CUSTIC
software accepts meteorological data records to define the conditions for sound
propagation. The model estimates the noise level for each source and receptor
combination and calculates user-selected averages.

For an external source, the noise level equation is

Leq=LW-20Log(r)-11dB(A)

where r is the distance and LW the source power.
However, for an industrial complex, the next equation will be used:

Leq=Li+10Log(S)-20Log(r)-14dB(A)

where S is the external surface and Li is the internal
noise power.

Noise
pollution map (colour gradient) in decibels dB(A) produced by roads.We
have 1000 vehicles per hour at a velocity of 50km/h. The red colour
represents high noise levels.